This course provides students an understanding of important human parasitic diseases, including their life cycles, vectors of transmission, distribution and epidemiology, pathophysiology and clinical manifestations, treatment, and prevention and control. Tropical Parasitology is taught by faculty from an area highly impacted by tropical parasites- the Kilimanjaro Christian Medical University College in Moshi, Tanzania. The faculty include Drs. Frank Mosha and Mramba Nyindo (and two lecturers, Drs. Johnson Matowo and Jovin Kitau). Dr. John Bartlett, Professor of Medicine, Global Health and Nursing at Duke University, joins his faculty colleagues in this effort.

JM

Its the nice course I am looking foward to see more courses like these, KCMUCO partnering with DUKE University

SM

Oct 27, 2018

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It was very interesting to hear from people who actually deal with these diseases on a daily basis.

À partir de la leçon

Trematodes

The Trematodes cluster focuses on schistosomiasis and fascioliasis. It is estimated that almost 60 million people are infested with trematodes globally. This cluster has a total of 79 minutes of video and 31 pages of reading spread out over the two lessons. You will have unlimited opportunities to take an untimed quiz after you’ve mastered the material in each lesson, and you have two quizzes to complete for this cluster. This cluster begins by looking at schistosomiasis, a common intravascular infection caused by parasitic trematode worms in contaminated water.

Franklin Mosha, Ph.D.

Mramba Nyindo, Ph.D.

Transcription

Now we're going to talk about schistosomiasis: pathophysiology, clinical manifestations and treatment. It's important to think about the timeline of schistosomiasis. It begins with cercarial invasion of the skin and migration of schistomules to the gut. Here they mature into schistosomes and commence egg laying. During established infection there is massive egg laying, and many of the late complications which occur decades later are due to these eggs and the inflammatory response to the eggs. In terms of the principles of schistosomiasis, it begins with the schistosomes invading the walls of the gut and the urinary tract. The damage is caused by the eggs. Half of the eggs are deposited in organ walls or enter the venous circulation. The other half of the eggs go directly into the lumen of the gut or the urinary tract. Because the eggs are relatively large, up to 70um, they embolize in the venous circulation, especially in portal venules or in pulmonary arterioles. There is a robust inflammatory response to tissue eggs marked by high levels of TNF-alpha and granuloma formation, and over time evolves to chronic inflammation and scarring. The late complications of schistosomiasis typically occur decades after infection. Schistosoma haemotobium mostly involves the urinary tract. Schistosoma mansonii mostly involves the gut, portal circulation, liver, and lungs. There may be some overlap between the two. In terms of the organs that are affected by schistosomiasis, it begins with an initial invasion of the skin. Then there's localization in the gut for Schistosoma mansonii and in the urinary tract for Schistosoma haematobium. This occurs within the first three months after infection. Schistosoma haematobium will be found in the bladder wall, ureter walls, genital tract and kidneys. Schistosoma mansonii will be found in the gut wall and periportal venules. This leads to periportal fibrosis, with a so called clay pipe pattern, which is the classic lesion of Schistosoma mansonii. Here we see a photo micrograph depicting periportal fibrosis. Here is the portal triad at the center of the screen. And you can see surrounding it a blue area that's typical for periportal fibrosis. So this is the classic lesion of Schistosoma mansonii infection. The chronic consequences of Schistosoma mansonii infection include portal hypertension with splenomegaly, esophageal varices, and ascites. You may also find patients who have colonic polyposis or a granulomatous pulmonary arteritis with pulmonary hypertension. During the acute phase of schistosomiasis, many patients are asymptomatic. However, some may complain of an urticarial and pruritic skin rash 1-3 days after exposure, so called swimmer's itch. During the dissemination phase of schistosomiasis, patients may complain of fever, abdominal pain and GI symptoms. This was classically described in the context of Schistosomia japonicum infection, and was known as Katayama fever, after the town in which it was described. During the chronic phase of schistosomiasis, most patients may be asymptomatic for decades until late complications arise. For Schistosoma haematobium in the chronic phase, painless hematuria is the classic symptom, and is frequently recurrent. Patients may also have urinary urgency, incontinence, obstruction or fistulae between the urinary tract and skin. Female genital tract lesions may lead to infertility and increased risk for HIV acquisition. Severe chronic disease may result in multiple fistulae. In the context of men, this may be called watering can scrotum. In the chronic phase, Schistosoma mansonii infection may result in chronic gastrointestinal complaints. On physical exam you may detect firm hepatomegaly, but you won't see findings of hepatocellular dysfunction. Splenomegaly may be quite dramatic, and patients may complain of left upper quadrant pain. Patients may have ascites. They may have upper GI bleeding due to varices associated with portal hypertension. And finally, they may have pulmonary hypertension. The laboratory findings and diagnosis of schistosomiasis are listed on this slide. Schistosoma haematobium is classically associated with hematuria, recurrent urinary tract infections, and renal insufficiency due to obstruction. Schistosoma mansonii frequently has no laboratory findings, and may have normal liver enzymes and liver function. The diagnosis is based on visualization of eggs in the urine or stool. In chronic disease, rectal biopsy may be due, may be needed to establish the diagnosis due to a lower egg burden. The treatment for schistosomiasis includes Praziquantel as the favored option. The prognosis is excellent, and a single dose of praziquantel 40mg/kg cures 80% of infected persons. Follow-up urine or stool specimens should be collected at 6 to 8 weeks and 6 months to ensure clearance of the eggs. In patients who have concurrent tuberculosis, be aware that praziquantel may interact with isoniazid and rifampicin. Now I'd like to share with you a typical case history. A 50 year old man was admitted to hospital with progressive abdominal swelling. On exam, his abdomen was protuberant, and he had shifting dullness, typical of ascites. A firm liver edge was palpable two centimeters below his right costal margin and his spleen tip was palpable near his umbilicus. He had no secondary signs of hepatic dysfunction. His liver enzymes and measures of hepatic synthetic function were normal. A stool sample revealed eggs of Schistosoma mansonii. He received praziquantel, 40mg/kg as a single dose. The next day he experienced massive hematemesis, and became hypotensive. Urgent endoscopy revealed esophageal varices and he underwent a banding procedure. Following stabilization of his blood pressure, he began propranolol to treat his portal hypertension. Follow up stool specimens revealed no eggs. This is a common presentation for chronic Schistosoma mansonii infection, with no symptoms except for progressive abdominal distension. A rapid diagnosis of Schistosoma mansonii infection was established and treatment prescribed. His portal hypertension will take time to reverse, but his portal pressures will decrease with time.